The invention relates to a rotor structure for rotary wing aircraft, especially helicopters in which the rotor blades are respectively connected to a carrier beam or bar in a non-rigid manner and without any flapping and lagging hinges. The carrier bar is supported by the rotor head. A bending moment is effective at each rotor blade or wing as a result of the centrifugal force. The just mentioned bending moment is effective in a direction opposite to the bending moment produced by the forces of the air. Under normal or rated operating conditions the bending moment caused by the forces of the air is balanced by the bending moment caused by the centrifugal force, as far as the static moment components are concerned in the area of the blade connection to the rotor head.
In connection with rotors for rotary wing aircrafts, especially helicopter main rotors, it is known to arrange the blades in such a manner that the longitudinal wing or blade axis extends at a fixed angle, the so-called cone angle, so that the center of gravity of the wing is located, on the average, so far above the blade connection point that a torsional moment balance establishes itself at the rated load and rated r.p.m. of the rotor in the area of the blade connection point, said balancing being accomplished between the bending moment produced by the centrifugal force effect due to the elevated center of gravity and between the bending moment resulting from the forces of the air. The foregoing applies, as mentioned, particularly to the main rotor of a helicopter in which the rotor blades are rotatably supported by a blade angle bearing secured to the rotor head and permitting the angular movement necessary for the adjustment of the pitch angle.
For the purpose of achieving said balancing, the longitudinal blade or wing axis and the axis of the blade angle bearing are arranged coaxially relative to each other. In addition, the just mentioned two axes extend together at the so-called cone angle relative to the rotational plane of the rotor, said cone angle being within the range necessary for the balancing of the bending moments. In this connection reference is made to British Pat. No. 639,572 and German Pat. No. 1,531,375. This type of arrangement has manufacturing disadvantages because it is necessary to adapt the supporting elements of the rotor head including the respective rotor head bores to said angular or slanted position unless the cone angle is located in the area of the blade connection. Where blade angle bearings are used such locating of the cone angle, means that the blade connection point is positioned radially outwardly of the blade angle bearing. In that instance the respective angle is the so-called pre-droop angle. On the one hand, this type of arrangement simplifies the construction of the rotor head where the center line of the carrier beam extends perpendicularly to the rotational axis of the rotor and where a control axis cone angle results which has an angular value of zero degrees. However, the longitudinal axis of the wing or blade travels, due to motions adjusting the pitch angle, on a straight circular cone having a relatively large opening angle which corresponds to the cone angle necessary for the complete bending moment balance. As a result, the blade or wing performs simultaneously with the pitch angle adjusting movement, movements in the lagging direction which increase in the direction toward the wing tip. Such movements are disadvantageous, especially with regard to the control or steering characteristics of the rotor.